The invention relates generally to apparatus and methods for controlling the flow of a polymer melt, and in particular, controlling a polymer melt flow with the use of a spool valve.
Hot runners are used in injection molding to deliver polymer melt from the nozzle of the injection molding machine to the mold cavity. Typically, multiple drops and gates are used in a hot runner system to deliver the melt to a plurality of locations in the mold so as to form multiple parts from corresponding cavities, or to form complex parts that require injection of the melt at multiple locations in a single cavity.
In conventional feed systems, the volumetric flow rate and pressure of polymer melt is determined by the design of the feed system. Once machined, conventional feed systems are unable to significantly change the behavior of flow entering the cavity at one location without similarly affecting the flow of plastic at other locations or retooling the feed system. As such, the molder is sometimes limited in achieving the desired quality or economic performance in a molding application.
To achieve greater process flexibility and consistency, systems have been developed to dynamically control the pressure at multiple points in a feed system by varying the gap between the bore of a hot runner and an axially displaced valve pin. While the resulting methods provide improved process flexibility and consistency, the performance of these systems are limited by complexity, cost, size, shear degradation, energy consumption, and maintenance issues associated with the system's conceptual design.